Op just to close the loop here. Shorted contactors for both. 🤷‍♀️

Thanks to everybody who wrote with ideas. I finally climbed into the attic today (when it wasn’t so hot). No leak. Flashing light code indicates a low voltage (24V) short. HVAC company coming out tomorrow, hopefully it’s easy to find the issue.

If both are out, don't bother replacing the thermostats. That's an easy job, but it's not going to fix the problem. You either have a loose wire (assuming both thermostats share a wire at some point). Or there are some things that will turn off the unit for safety.

In our case, the float (the device at the hvac line where condensate water is pushed out -- the float in the line that goes up or down depending on how much water is in there) was old and got jammed permanently in 'up' position, suggesting there was too much water in the exit line. Every time it got jammed up, the thermostat shut off.

Check all of your outlets to see if you have a tripped gound fault outlet somewhere.

When something weird and random loses power, and no fuses are tripped, it is often one of those outlets somewhere.

Anonymous wrote:Thermostats (main level and basement) are blank! Do I call the hvac company or electrician?

I checked the breaker, and it is fine. Is this something simple that I might be able to fix?

Thank you for any advice!

Sure, it's an easy DIY thing to do. Just unscrewing old ones and mounting new ones with a couple wires to hook up. Not much different than changing a light bulb.
Plenty of videos on youtube I'm sure, if you can wade through the 10 min of drivel to explain a 2 min job.

Anonymous wrote:

Anonymous wrote:Two more things to check
1 does outside unit have circuit breaker outside to
check
2 is there any water or floor flood protection cutoff device that could have been jostled or tipped thus cutting off system see if there are any and reset then

Thank you. Would these cause the ac not to work, and the thermostat to be blank, or just the former?

Will check in any case. Thank you!

Thermostat on ours is blank if system is shut off or cut off. The system also isn't running.
IF I turn the system off properly thermostat is not blank.

Anonymous wrote:

Anonymous wrote:Did you replace the battery?

I opened up the thermostat. I think it’s hardwired and not battery operated.

If it is programmable it usually has a battery even if it is hardwired. Just look up the model online. It will also give you troubleshooting steps.

Anonymous wrote:Thermostats (main level and basement) are blank! Do I call the hvac company or electrician?

I checked the breaker, and it is fine. Is this something simple that I might be able to fix?

Thank you for any advice!

When I had this happen it turned out that the outlet into which the AC condensate pump was plugged had gone bad. Once the water level was too high the thermostat went blank. The HVAC company helped me troubleshoot over the phone and then told me to call the electrician.

Anonymous wrote:Two more things to check
1 does outside unit have circuit breaker outside to
check
2 is there any water or floor flood protection cutoff device that could have been jostled or tipped thus cutting off system see if there are any and reset then

Thank you. Would these cause the ac not to work, and the thermostat to be blank, or just the former?

Will check in any case. Thank you!

If you have a heat pump it is probably the water shutoff trigger. Easy fix.